This invention relates to a bone cement applicator for delivering a predetermined amount of cement into a bone to achieve substantially uniform penetration of cement over a predetermined surface-area of the bone, particularly the top of a resected tibia. The invention is also concerned with a method of applying bone cement using such applicator.
The use of prosthetic components involving the cementing of such components to bone, particularly total knee replacement, is taking place with increasing frequency. Accordingly, there is increasing interest in the improvement of cementing techniques to avoid complications arising from loosening of the prosthetic component.
When a prosthetic component is attached to cancellous bone with bone cement, particularly acrylic cement, a bond is formed by the penetration of the cement into the bone. The depth of penetration is dependent upon the pressure under which the cement is applied, the time of pressure application, the viscosity of the cement and the porosity of the bone; and the said depth is a predominant factor in determining the tensile or shear strength of the cement-bone interface.
A problem with total knee replacement is that prosthetic loosening frequently occurs. Loosening of the tibial component has been a serious problem with many of the early prosthetic knees. Such loosening leads to instability and pain. In cases where the loosening was such as to require revision invariably radiolucency was observed at the cement-bone interface. This radiolucency normally signifies a layer of fibrous tissue beneath which is often a thin layer of dense bone. Loose prosthetic components together with cement usually may be lifted from the surface of fibrous tissue, indicating that there is zero tensile bond strength at the interface. Presumably, an initial cement-bone interface of low tensile strength which allowed micromovements to occur between the cement and bone would readily reach this condition, whereas a high initial tensile strength tends to inhibit interface breakdown.
Various methods have been developed to improve the cementing technique and consequently increase the strength of the bone-cement interface in total knee replacement and thus avoid tibial component loosening. However, although relatively good cement penetration has been achieved by past methods in the central areas of the tibia, in contrast, the periphery often shows poor penetration secondary to leakage of cement around the component on insertion. In the past it has proved difficult to achieve adequate cement penetration in sclerotic bone resulting from valgus or varus deformity. These peripheral and sclerotic areas are the earliest and most frequent sites of radiolucencies at the bone-cement interface.
Accordingly, it is an object of the present invention to provide means whereby uniform cement penetration over the entire bone surface is achieved.